Digital logic circuits frequently rely on clock signals for synchronization, derivation of reference signals, measuring phase differences, and other functions. Some applications require a quadrature clock that has a 90° phase difference from a reference clock. A quadrature clock is frequently used for strobe signals, for example.
A centralized quadrature clock may be generated and distributed to all components. In particular, a first clock and a second clock having a 90° phase difference from the first clock are centrally generated and distributed. One disadvantage of this approach is that clock signals tend to have constraints that are difficult to maintain throughout the distribution when the distribution is over a relatively large area or used to drive a relatively large number of components. For example, significant consumption of die area and wire routing resources are required to meet skew requirements for both clocks in integrated circuit applications. The use of some types of integrated circuit logic in the clock distribution buffers may even result in a doubling of the power consumption due to the distribution of two clocks.
Another technique for generating the quadrature clock entails distributing a reference clock signal to regions of an integrated circuit. Each region has a local phase locked loop (PLL) or local delay locked loop (DLL) to derive the quadrature clock signal from the reference clock signal. A disadvantage of this approach is that the localized PLLs or DLLs introduce complexity into the integrated circuit design thus incurring more design and verification time. In addition, co-ordinating selection from the reference clock of the proper phase associated with the first and second clocks across all regions such that the first clock in one region is in phase with the first clock of another region is problematic.